1. Field of the Invention
The present invention relates to catalysts and processes for treating heavy feedstocks such as petroleum residuum. The invention more particularly relates to catalysts suitable for promoting hydrocracking reactions which convert such feedstocks to products having relatively lower boiling temperatures, to processes for making and using the catalysts, and to processes for using such catalysts.
2. Description of the Prior Art
Maximizing the yield of highly-valued products from crude oil often results in the production of relatively heavy hydrocarbon streams which are difficult to up-grade to lighter products. Typically, these streams are distillation bottoms resulting from the atmospheric or vacuum distillation of a crude oil or a crude oil-derived feedstream. These bottoms fractions are known as petroleum residuum or "resid." Resids typically contain only a small amount of material boiling below about 1000.degree. F. at atmospheric pressure, up to several tens of percent of Ramsbottom carbon, and up to several hundred parts per million of metals such as nickel and vanadium.
Modern refinery economics demand that resids be processed to yield lighter and more valuable hydrocarbons. Typically, resid will be upgraded in a multi-reactor, supported catalyst system such as those described in U.S. Pat. Nos. 4,940,529 issued to Beaton et al; 5,013,427 issued to Mosby et al.; 5,124,025 issued to Kolstad et al.; 5,124,026 issued to Taylor et al.; and 5,124,027 issued to Beaton et al., all assigned to the assignee of the present invention, the disclosures of which are hereby incorporated by reference. While supported catalyst systems such as those disclosed in the foregoing patents have proven highly effective in upgrading heavy feedstreams such as resids, refiners continue to investigate other processes for obtaining valuable products from resids.
Another approach for upgrading resid is to hydrocrack resid in the presence of a soluble catalyst which is eventually precipitated to produce a solid catalyst dispersed as, for example, a suspended bed or an ebullating bed. This approach is described, among other places, in U.S. Pat. No. 5,055,174 issued to Howell et al.; U.S. Pat. No. 5,446,002 issued to Kukes et al.; and U.S. Pat. No. 5,489,375 issued to Joseph et al., which are hereby incorporated by reference. Although the soluble catalyst is at least initially soluble in a feedstock or a carrier liquid, the soluble catalyst is generally precipitated to provide a dispersion of fine solids, such as metal disulfide particles, in the reactor.
Other researchers have reported that the presence of additional particulate matter tends to suppress coke production within a resid hydrocracking reaction zone that includes a fine catalytic dispersion of the type which may be precipitated from a soluble catalyst. U.S. Pat. No. 4,178,227 issued to Metrailer et al.; U.S. Pat. No. 4,376,037 issued to Dahlberg et al.; U.S. Pat. Nos. 4,770,764 and 4,863,887 issued to Ohtake et al.; and U.S. Pat. No. 5,320,741 issued to Johnson et al., which are hereby incorporated by reference, describe catalyst systems which contain fine contact particles and a dispersed precipitate from a soluble catalyst. U.S. Pat. No. 4,406,772 issued to Sasaki et al. describes a hydroconversion process which converts heavy hydrocarbon oils such as vacuum residua into light hydrocarbon oils, employing a catalyst which is obtained as a byproduct of the process. The catalyst includes coke produced by the hydrotreatment and a metal belonging to Groups VB or Group VIII of the Periodic Table, such as iron, vanadium, or nickel, which is derived from the heavy hydrocarbon oils and deposited on the coke during the hydrotreatment.
Canadian Patent No. 1,207,265 listing Graeser et al. as inventors describes a method for hydrogenating heavy oil in the presence of a catalyst which is the soot obtained from gasification or partial combustion of heavy oil or solid fuel. The soot is reportedly actuated by treatment with carbon monoxide, carbon dioxide, or water at high temperatures in order to obtain a relatively great internal surface area which is said to facilitate adsorptive binding of the soot to coke particles. The Graeser et al. patent also reports that the activity of the catalyst can be increased by impregnating the soot with a salt of one or more catalytically active metals, especially titanium, chromium, iron, cobalt, nickel, tin, or lead.
Open Japanese Patent Application No. 4-122790 listing Matsui as inventor appears to describe a process for catalytically hydrogenating heavy oil which contains polycyclic aromatics, such phenanthrene, to produce monocyclic or bicyclic aromatics. The Matsui application states that the source material can be produced from coal tar, oil sand tar, petroleum heavy oil or biomass tar. Reportedly, the active ingredient of the catalyst is cobalt, molybdenum, nickel, or tungsten. The metal is apparently sulfided before use. The Matsui application also states that a porous material such as alumina, silica-alumina, silica, or carbon black can be employed as a carrier for the active ingredient.
To facilitate the cost-efficient upgrading of hydrocarbon feedstocks such as resid, new catalysts and processes are required which minimize catalyst preparation costs and maximize the effectiveness of soluble catalysts under the aggressive operating conditions typically required to produce substantial quantities of lighter, more valuable products from a heavy hydrocarbon feedstock such as resid.